1. Field of the Invention
The present invention relates to a miniature type linear guide apparatus including a guide rail and a slider linearly movable by being guided by the guide rail through a plurality of steel balls interposed between the guide rail and the slider and, in particular, to a return guide fixing structure for a miniature type linear guide apparatus.
2. Description of the Art
A prior art miniature type linear guide apparatus includes a guide rail having ball rolling grooves formed in both lateral sides and a slider movably straddling the guide rail. The slider consists of a slider main body and end caps respectively joined to opposite ends of the slider main body. The slider main body has ball rolling grooves respectively opposing the ball rolling grooves of the guide rail and ball return passages respectively in parallel with the ball rolling grooves of the slider main body. On the other hand, each end cap has a pair of semicircular curved paths for bringing the ball rolling grooves into communication with the ball return passages. Thus, the slider is formed with a pair of ball infinitely circulating routes, each including the ball rolling grooves, the ball return passage in parallel with the ball rolling grooves, and the curved paths connecting the ball rolling grooves and the ball return passage. The slider is movable relative to the guide rail in an axial direction through the rolling of the plurality of balls.
In the case of a standard size linear guide apparatus, each of curved paths formed in an end cap has a half-doughnut shape so that balls make a smooth U-turn. Specifically, a pair of semicircular grooves are formed in a joining surface of the end cap and return guide fitting grooves having a half-cylindrical shape are formed respectively across the semicircular grooves. A half-cylindrical return guide is fitted into each of the return guide fitting grooves to form the curved path having the half-doughnut shape. The half-cylindrical return guide has projections formed on opposite ends. The return guide is fixed in the return guide fitting groove by using the projections as interferences.
In the case of the miniature type linear guide apparatus, as compared with the standard size linear guide apparatus, since it is very small in size, a sufficient space for the return guide is not available. As a result, the curved path formed in the end cap remains in its semicircular shape without being formed in the half-doughnut shape. Thus, no return guide is attached. For this reason, in some cases, the U-turn of the balls is not smooth. Accordingly, the inventors of the present application previously tried to make the U-turn of the balls smooth and, as shown in FIG. 6, a return guide fitting groove 11 is formed in an end cap 9 of a miniature type linear guide apparatus. A half-cylindrical return guide G having projections g1 as in the case of the standard size linear guide apparatus is attached to the return guide fitting groove 11.
However, since the space or area is not sufficient, at a lower end side of the return guide fitting groove 11 having a half-cylindrical shape, the wall thickness t of the end cap 8 becomes thin. As a result, when the return guide G is fitted into the return guide fitting groove 11, the thin wall portion of the end cap 8 is deformed and the fixing of the return guide G is not satisfactory. Accordingly, when the end cap 8 is attached to the slider main body, the return guide G falls off the end cap 8 and a problem is encountered in that the assembling work is inconvenient.
Furthermore, another problem is involved in that since the return guide G cannot be completely secured, the return guide G is loose and the smooth rolling movement of the balls is not insured, and the smooth operation of the linear guide apparatus cannot be achieved.